Evaluation of carbon reduction options in industrial combined heat and power plants

Abstract

Industry is a major contributor to the rise in global CO2 emissions, constituting one fifth of the global energy consumption, of which significant amount is provided by fossil fuel combustion. Following the Paris agreement, emphasis has been made on decarbonization of the industrial sector. This thesis focuses on industrial decarbonization by employing Carbon Capture and Storage for Combined Heat and Power (CHP) gas turbine plants. The scope of this thesis includes conceptual modelling and thermodynamic analysis of potential decarbonization options for zero carbon CHP plants. The studied options include post-combustion capture, exhaust gas recirculation, pre-combustion capture and oxyfuel combustion. As conventional air Brayton cycles are not applicable for oxy-fuel combustion in gas turbines, different working fluids and cycle configurations are proposed and thermodynamic performance is evaluated. Selected cycles were then compared based on thermodynamics, economics and off-design performance at a typical constant power to heat ratio of 0.78. It was observed that oxyfuel CHP cycle with CO2 working fluid is a promising solution for zero carbon CHP with 100% CO2 reduction. However, this solution requires new turbomachinery design. In view of this, a retrofit analysis is also performed in this thesis which evaluates if an existing air designed gas turbine can be used for CO2 operation. It was concluded from this analysis that it is possible to operate an air gas turbine on CO2 by incorporating proposed modifications of higher compressor inlet temperature (473K) and a turbine inlet nozzle area 20% larger than design. These modifications, however also lead to serious performance deterioration.